EFFECTS OF POLYETHYLENE-GLYCOL ON THE COORDINATION SPHERE OF STRONTIUM IN SRCL2 AND SR(NO3)(2) COMPLEXES

The reactions of SrCl2.6H(2)O or Sr(NO3)(2) in CH3CN (in the presence of NH4OH(aq)) with polyethylene glycols (PEGs: triethylene glycol(EO3) , tetraethylene glycol (EO4), pentaethylene glycol (EO5), or hexaethyl ene glycol (EO6)) in 1/1 stoichiometries lead to the isolation of dire ctly coordinated complexes. X-ray structural analyses of nine of these complexes have been carried out. The chlorides crystallize as discret e ions with the strontium cations surrounded by 8-10 oxygen donors and the chloride ions hydrogen bonded in the lattice. The EO3 and EO4 com plexes have a 2/1 PEG/Sr2+ stoichiometry while the EO5 and EO6 complex es can support only a 1/1 ratio but complete the Sr2+ coordination sph ere with H2O molecules. Both a hydrated and an anhydrous form of the E O4 complex were isolated. Cell data for the five SrCl2/PEG complexes a re as follows. [Sr(EO3)(2)]Cl-2 (C222(1)) (at 19 degrees C): a = 8.737 (4) Angstrom, b = 18.609(9) Angstrom, c = 12.548(9) Angstrom, and D-ca lc = 1.49 g cm(-3) for Z = 4. [Sr(EO4)(2)]Cl-2 (C2/c) (at 20 degrees C ): a = 17.528(9) Angstrom, b = 9.209(3) Angstrom, c = 17.180(9) Angstr om, beta = 121.13(8)degrees, and D-calc = 1.53 g cm(-3) for Z = 4. [Sr (EO4)(2)]Cl-2.3H(2)O (P2(1)/n) (at 19 degrees C): a = 12.225(7) Angstr om, b = 18.336(9) Angstrom, c = 12.258(9) Angstrom, beta = 90.25(5)Ang strom, and D-calc = 1.45 g cm(-3) for Z = 4. [Sr(OH2)(3)(EO5)]Cl-2 (P ($) over bar 1) (at 18 degrees C): a = 8.217(9) Angstrom, b = 9.000(8) Angstrom, c = 14.514(8) Angstrom, alpha = 75.55(6)degrees, beta = 83. 33(7)degrees, gamma = 69.59(9)degrees, and D-calc = 1.54 g cm(-3) for Z = 2. [Sr(OH2)(2)(EO6)]Cl-2.H2O (P2(1)/n) (at 18 degrees C): a = 9.74 1(6) Angstrom, b = 16.534(3) Angstrom, c = 13.600(4) Angstrom, beta = 100.16(4)degrees, and D-calc = 1.52 g cm(-3) for Z = 4. The Sr(NO3)(2) /EO4-EO6 complexes all crystallize as tight ion pairs with trans nitra tes and a nearly equatorial girdle of oxygen donors. To three structur ally characterized complexes all have 1/1 PEG/Sr2+ stoichiometries and are all 10-coordinate., The achieve 10-coordination the EO4 complex c rystallizes as a monohydrate and in the EO6 complex the ligand is only hexadentate. The Sr(NO3)2/EO3 complex is also 10-coordinate but achie ves this with two coordinated glycols and one bidentate nitrate anion. The second unique anion is hydrogen bonded to the glycols. Cell data for the four Sr(NO3)(2)/PEG complexes are as follows. [Sr(NO3)(EO3)(2) ] [NO3] (P2(1)) (at 20 degrees C): a = 8.156(2) Angstrom, b = 9.992(1) Angstrom, c = 13.158(2) Angstrom, beta = 92.09(1)degrees, and D-calc = 1.59 g cm(-3) for Z = 2. [Sr(NO3)(2)(OH2)(EO4)] (P ($) over bar 1) ( at 18 degrees C): a = 7.911(2) Angstrom, b = 9.810(3) Angstrom, c = 10 .917(3) Angstrom, alpha = 92.43(3)degrees, beta = 94.02(2)degrees, gam ma = 91.75(2)degrees, and D-calc = 1.67 g cm(-3) for Z = 2. [Sr(NO3)(2 )(EO5)] (P ($) over bar 1) (at 18 degrees C): a = 9.330(9) Angstrom, b = 10.060(9) Angstrom, c = 11.684(5) Angstrom, a = 67.86(8)degrees, be ta = 68.04(8)degrees, gamma = 68.18(9)degrees, and D-calc = 1.65 g cm( -3) for Z = 2. [Sr(NO3)(2)(EO6)] (P2(1)/c) (at 19 degrees C): a = 16.2 04(8) Angstrom, b = 10. 760(4) Angstrom, c = 12.365(2) Angstrom, beta = 106.91(4)degrees, and D-calc = 1.59 g cm(-3) for Z = 4. In all nine complexes, the glycols have fairly similar conformations and tend to f orm pseudocyclized in-cavity crown ether-like complexes. The average S r-O(alcoholic) and Sr-O(etheric) separations range from 2.526(6) to 2. 67(2) A and from 2.603(1) to 2.74(5) A, respectively.